The present invention relates in general to semiconductor devices and, more particularly, to switch mode power supplies used in battery chargers.
The global nature of technology creates a demand for xe2x80x9cuniversalxe2x80x9d devices that can operate in most if not all countries. For example, portable devices such as notebook computers and digital cameras can operate in multiple countries because they are powered from batteries rather than a local alternating current (AC) power source. However, the battery chargers used to recharge the batteries do operate from a local AC power source, and therefore often do not operate in multiple countries due to different AC power standards. Worldwide, AC power is provided at a voltage level ranging from about eighty volts root mean square (RMS) to about three hundred sixty volts RMS.
A battery charger typically includes a power supply whose integrated circuits and other electrical components process the incoming AC power to produce a direct current (DC) supply voltage for charging a battery. However, many of the power supplies"" components cannot function over the necessary voltage range. A charger configured to operate at two hundred volts RMS may incur damage if used in a country providing three hundred volts RMS. On the other hand, if the AC power provides only eighty volts RMS, the components may not receive enough voltage to function correctly, which can damage the battery.
Most previous power supplies function over a limited voltage range, and therefore can operate in only one country. Chargers using these power supplies have a high cost because manufactures use different designs and/or components for each country, thereby losing the economy of scale. Other battery chargers can operate in multiple locations but require external controls such as user-operated switches to select an AC voltage appropriate for the location. Such chargers have lower design costs but are susceptible to damage if a user inadvertently selects the wrong voltage level. The external controls are inconvenient for the user and also increase the component count, which increases the fabrication cost of the charger.
Hence, there is a need for a circuit and method of providing a supply voltage which can operate from a wide range of supply voltages without incurring damage while reducing the manufacturing cost by reducing the number of external user controls.